Structural tunability of Co-based nanoMOFs by modulator controls catalytic performance of aqueous dye pollutants

This work explores the role of CTAB as a surfactant, stabilizer, and modulator in determining the structural characteristics as morphology and size of ZIF-67 nanoMOFs. Furthermore, the influence of these structural changes on the physico-chemical and catalytic properties of the derived nanostructures is analyzed. By modifying the CTAB concentration in the synthesis process, ZIF-67 experienced a morphological transition from perfectly cubic, monodisperse nanoparticles with edge sizes of ca. 80 nm at the highest CTAB concentration used (4 mM) to cross-spike or flower-like structures within the micro size range in its absence, without evident changes in the inherent MOF sodalite-type structure with high thermal stability and crystalline structure. The activation of peroxymonosulphate (PMS) as oxidizing agent by these nanoMOFs to degrade RhB proved to be highly effective achieving very large efficiencies (>95 %). Several factors affecting PMS activation were also evaluated, such as catalyst concentration, pH, temperature, UV irradiation and ultrasonication. Optimal conditions for RhB degradation included slightly acidic pH, high temperature (65 °C) and UV light (365 nm). It was also observed that the ZIF-67 nanocube morphology showed lower catalytic activity in comparison with the flower-like structures. ZIF-67 nanoMOFs also showed potential as photocatalysts under visible light irradiation. As the concentration of CTAB increased during the synthesis, the range of allowed bandgap energies progressively decreases. This change correlates with a change in the electronic properties of the nanomaterial, which can affect its ability to absorb and utilize visible light for photocatalytic reactions.